The latest developments of the 3GPP standards are referred to as the Long Term Evolution (LTE) of EPC (Evolved Packet Core) network and E-UTRAN (Evolved UMTS Terrestrial Radio Access Network). Under the 3GPP standards, a NodeB (or an eNB in LTE) is the base station via which communications devices connect to a core network and communicate to other communications devices or remote servers. For simplicity, the present application will use the term base station to refer to any such base stations. Communications devices might be, for example, mobile communications devices such as mobile telephones, smartphones, user equipment, personal digital assistants, laptop computers, web browsers, e-book readers and the like. Such mobile (or even generally stationary) devices are typically operated by a user. However, 3GPP standards also make it possible to connect Machine-Type Communications (MTC) devices (sometimes also referred to as Machine-to-Machine (M2M) communications devices) to the network, which typically comprise automated equipment, such as various measuring equipment, telemetry equipment, monitoring systems, tracking and tracing devices, in-vehicle safety systems, vehicle maintenance systems, road sensors, digital billboards, point of sale (POS) terminals, remote control systems and the like. MTC devices can be implemented as a part of a (generally) stationary apparatus such as vending machines, roadside sensors, POS terminals, although some MTC devices can be embedded in non, stationary apparatus (e.g. vehicles) or attached to animals or persons to be monitored/tracked.
For simplicity, the present application refers to MTC devices in the description but it will be appreciated that the technology described can be implemented on any communications devices (mobile and/or generally stationary) that can connect to a communications network for sending/receiving data, regardless whether such communications devices are controlled by human input or software instructions stored in memory.
MTC devices connect to the network to send to or receive data from a remote ‘machine’ (e.g. a server) or user. MTC devices use communication protocols and standards that are optimised for mobile telephones or similar user equipment. However, MTC devices, once deployed, typically operate without requiring human supervision or interaction, and follow software instructions stored in an internal memory. MTC devices might also remain stationary and/or inactive for a long period of time. The specific network requirements to support MTC devices have been dealt with in the 3GPP TS 22.368 standard, the contents of which are incorporated herein by reference.
Some MTC devices are deployed at remote, hazardous, or concealed locations or at locations with restricted access. In addition, they might be deployed in a high number and over a large geographical area (e.g. tsunami detection sensors). MTC devices are thus generally designed to be able to operate without human supervision and for as long as possible. For example, MTC devices can be programmed to autonomously set up a connection to report an event and then to go back to a low-power mode of operation, such as a sleep mode, stand-by mode, and the like.
Power consumption is a highly important aspect of all mobile terminals relying on battery power and also mobile terminals using an external power supply. Its importance increases with the continued growth of MTC device population and their more demanding use cases. In the case of certain Machine to Machine (M2M) applications, e.g. sensors that are running on battery power, the on-site exchange (or recharging) of the batteries of a large number of devices can represent a significant expense for MTC device owners/operators. Furthermore, the battery lifetime can determine the device's lifetime or useful operational time if it is not possible to charge or replace the battery cost effectively.
In a battery powered communications device, battery life reduces with increased transmission power. In 3GPP networks, power control is used in order to reduce transmission power and overall interference. For example, a mobile terminal that is located close to its serving base station (and/or experiencing generally good signal propagation characteristics) transmits using a relatively low power, whilst a mobile terminal that is located further away from the base station (and/or under bad propagation characteristics) transmits using relatively higher power, e.g. near to or at a maximum transmit power. This mechanism can be used to improve battery life for mobile terminals that are located near their serving base station most of the time (typically, for example, in an urban environment with good network coverage) because they rarely have to transmit using their maximum transmission power. However, a principal goal of the above 3GPP power control scheme is not to conserve battery power but to balance the signal quality of each physical link at the base station's transceiver, thereby maximising the overall system capacity.